regarding express courrier like FED EX and UPS.
The first one is that I was referring to documents so the cargo is paper
Don't assume that express couriers fly just paper documents. These days most of those go by email while express freight is made up of just about any urgent stuff you can imagine from pharmacuticals to car parts. Electronics to frozen fish. The majority of it though is high volume low density (people use big carboard boxes stuffed with polystyrene, for obvious reasons.)